1. Field of the Invention
The present invention relates to a dental restorative material composition which is properly used for filling and restoring a cavity of a dental caries.
2. Description of the Conventional Art
A dental restorative material composition, e.g., a dental composite resin, has been required to have X-ray contrast imaging property in order to confirm it after a dental treatment. A dental restorative material composition generally includes a monomer to be a base material at the time of a polymerization, a filler such as a glass powder, and a polymerizing catalyst to harden the monomer. A glass powder as a filler has a maximum particle diameter of 1 to 2 μm. In the conventional dental restorative material composition, a dental restorative material after hardening obtains X-ray contrast imaging property by blending a material having X-ray contrast imaging property in the glass powder.
However, a glass powder having a maximum particle diameter of 1 to 2μm has a problem that a dental restorative material composition becomes easily sticky, that is, when the composition is filled in a tooth by using an exclusive spatula, the composition is adhered to the spatula so that operativity decreases. Since this glass powder has a large specific surface area of a particle, it is necessary to include a large amount of monomer component in a dental restorative material composition. Thus, the ratio of the glass powder occupying in a dental restorative material composition decreases. As a result of this, there is a problem that a dental restorative material after hardening is largely shrunk by polymerization.
In order to improve the above-described sticky problem and large polymerization shrinkage problem, for example, Japanese Unexamined Patent Publication No. 5-194135 discloses a dental restorative material composition using an organic-inorganic composite filler having an average particle diameter of 5 to 50 μm made by mixing a monomer and a glass powder having a particle diameter of 1 to 2μm, polymerizing and hardening the mixture, and pulverizing it. However, it is hard to obtain high X-ray contrast imaging property by only the glass powder. Further, when a glass powder is used, a composition is influenced by refractive index of the glass powder, and thus it is necessary to adjust a refractive index of a glass powder with a refractive index of a product after polymerization. However, since the refractive index of a monomer is varied by polymerizing and hardening the monomer, a relationship between the refractive indexes of a glass powder and a monomer is varied after and before hardening those, and thus transparency is damaged.
When a particle diameter of a filler is smaller, a dental restorative material composition is more hardly influenced by a refractive index of the filler. Thus, for example, Japanese Patent Publication No. 3-10603 and Unexamined Japanese Patent Publication No. 10-130116 disclose a composite resin using an organic-inorganic composite filler made by mixing a monomer and a fine particle filler having an average primary particle diameter of 0.005 to 0.04 μm, polymerizing and hardening the mixture, and pulverizing it. However, organic-inorganic composite fillers using a fine particle filler in these prior arts use colloidal silica not having X-ray contrast imaging property as the fine particle filler. Thus, there is a problem that there is almost no X-ray contrast imaging property required for a dental restorative material composition.
On the other hand, in order to give X-ray contrast imaging property to the composition, for example, Japanese Translation of PCT Publication No. 2003-512407 discloses a dental restorative material composition made by directly blending a material, e.g., a metal oxide or a metal fluoride, with a composition as a filler. However, when the metal oxide or metal fluoride has an average particle diameter of 0.5 to 1 μm, a refractive index of the metal oxide or the metal fluoride is not adjusted with the refractive index of a monomer after hardening, and thus there is a problem that a hardened dental restorative material composition cannot has similar transparency to that of a natural tooth. Even in the case of using a material, e.g., a metal oxide or a metal fluoride, having an average particle diameter of less than 0.5 μm, if the material is not blended in an organic-inorganic composite filler but is directly mixed in the composition, there is a still problem that operativity of the composition is inferior like the case of the conventional fine particle filler.